Method for pressure bonding of a breaker-tread assembly with a carcass assembly by means of stitching in the manufacture of green tyres and device for accomplishment of such method

ABSTRACT

Described is a method of joining a belt-tread assembly with a carcass assembly by stitching in green tire production such that a pressure is applied in radial inward direction on the rotating outer peripheral surface of a belt-tread assembly ( 5 ) partially joined with an inflated carcass assembly ( 1 ) of a tire, which is disposed on a tire building drum, the pressure being exerted by inelastic force of at least two stitching rollers ( 2 ) which are rotationally and inelastically disposed on a rigid bearing part ( 3 ) of the stitching unit. The rigid bearing part ( 3 ) is provided with means for mutual symmetrical axial movement in the direction of arrow ( 6 ) of the stitching rollers ( 2 ) from the central part of the outer peripheral surface of the belt-tread assembly ( 5 ) of the tire being produced to its shoulders, with means for moving the rigid bearing part ( 3 ) along an axis perpendicular to the rotation axis of the tire being produced, and with means controlling rotational position of the stitching rollers ( 2 ) in the direction of arrow ( 7 ), the compressive force of the rollers ( 2 ) being controlled by the means for moving the rigid bearing part ( 3 ) in the direction of an axis perpendicular to the rotation axis of the tire being produced. Also a device for accomplishing the method is described.

A method for pressure-bonding of a breaker-tread assembly with a carcassassembly by means of stitching in the manufacture of green tyres anddevice for accomplishment of such method

The present invention concerns a method of joining belt-tread assemblywith carcass assembly in green tyre production, carried out by pressinga belt-tread assembly radially inwards against the outer peripheralsurface of an inflated ring carcass assembly, to achieve mutual joiningof the components. The invention concerns also a device for stitchingthe belt-tread assembly onto the carcass assembly, utilising the methodaccording to the present invention.

BACKGROUND ART

In the process of tyre production a carcass assembly is inflated andshaped on a tyre building drum, so that partial bonding with abelt-tread assembly, prepared in advance, is achieved. Subsequently, thetyre building drum is rotated so that also the belt-tread assembly isrotated together with the inflated carcass.

Final joining of the belt-tread assembly with the inflated carcassassembly is usually performed using compressive force exerted by anelastic cylinder on stitching rollers in radial direction.

Methods of joining a belt-tread assembly with an inflated carcassassembly, known so far, make use of a compressive force exerted inradial direction by an elastic pneumatic cylinder, on which dividedstitching rollers are disposed. The divided stitching rollers, differingin diameter, have a profile usually designed so as to press the surfaceof the tyre tread along its entire length.

A further method of joining a belt-tread with an inflated carcass, makesuse of a compressive force exerted in radial direction by an elasticpneumatic cylinder, on which a pair of stitching rollers is located. Thepair of stitching rollers gradually symmetrically moves by an axialmovement in parallel with the tyre axis from the centre to thebelt-tread edges.

There may be various design solutions for the stitching devices. Suchdevices may be designed, for example, as dynamic that is each of therollers rotates during stitching around its own axis which is parallelto the rotation axis of the tyre being produced and, simultaneously, therollers move mutually symmetrically in the direction from the centralpart of the outer peripheral surface of the tyre being produced to itsshoulders, i. e. the stitching rollers are moved in parallel with therotation axis of the tyre; such design solution can be found, forexample, in the patent EP 0 770 475 B1, where a system of two stitchingrollers disposed on pneumatic cylinders attached to a fixed support isused, wherein the movement of the support in radial direction and themovement of stitching rollers disposed on pneumatic cylinders in axialdirection is ensured by means of threaded rods connected with electricmotors. A device according to the above patent comprises also means fordeflecting the rotation axis of the stitching rollers from a positionparallel to the rotation axis of the tyre building drum.

A further type of stitching devices is constituted by static stitchingdevices in which, when used, rollers are moved only around their ownaxes without relative movement of the rollers used. A combination ofstatic and dynamic rollers is possible as well. It is described e.g. inthe patent EP 0 627 302 B1, where the subject-matter of the invention isa device for radial tyre production, a part of the device consisting ofa pressure unit provided with at least one roller. Specifically, thereare three rollers, wherein one of them being static presses down thecentral part of the outer peripheral surface of the tyre and two dynamicrollers are disposed so as to press down the belt-tread edges. Theserollers are moved by the action of a pneumatic cylinder into openings ofa transfer unit, which is adapted specifically for this purpose andtransfers the belt and tread from a winding drum to the tyre buildingdrum.

Static stitching rollers may be designed also as divided, havingdifferent diameters, and their profile allows to press down the tyretread surface along its entire width. However, also when using dividedstitching rollers, it is possible to make use also of the movement ofthe stitching unit with rollers in a direction parallel to the buildingdrum axis, as described, for example, in the patent SU 1305056 A1, whereeach single part of the divided stitching roller comprises a spring, sothat its position is not fixed, but can vary depending on the varyingsurface during axial movement of the divided roller relative to thebuilding drum axis.

By using the above devices it is possible to accomplish a method ofpressing down—stitching a belt-tread assembly to a carcass assembly,wherein in this case elastic elements acting in opposite directions comeinto contact, namely the inflated belt-tread assembly and the pneumaticcylinder with stitching rollers. If common surface non-uniformities ofthe rotating belt-tread occur, mutual interaction of stitching rollersand belt-tread arises. This interaction has an adverse effect on theuniformity of the produced tyres.

Disadvantages of the above methods consist in lower uniformity of theproduced tyres, deformation of carcass fibres, possibility of presenceof air pockets in the tyre shoulders and complicated adjusting of thestitching roller profile during dimension change of the produced tyres.

Now it has been surprisingly found that the above interaction betweentwo elastic elements, which consist of a pneumatic cylinder constitutinga part of the stitching unit containing at least one stitching rollerand of an inflated carcass assembly, can be reduced in such a way thatno elastic element, but instead a rigid inelastic element is used in thedesign of the stitching unit. Utilising the method and device accordingto the present invention higher uniformity of the produced tyres isachieved.

A method of green tyre production usually includes the followingoperations:

-   -   production of an integrated carcass assembly in the form of a        cylinder jacket, consisting usually of inner rubber, sidewalls        and carcass plies, and subsequent mounting of bead wires,    -   production of the belt-tread assembly in the form of a cylinder        jacket, usually consisting of several belt plies and a tread,    -   transferring the belt-tread assembly to a given position over        the carcass assembly,    -   shaping the carcass assembly into a toroidal shape by inflating        the assembly with simultaneous approaching the bead wires,        turn-up the carcass plies and sidewalls around the bead wires,        pressing the sidewalls of the tyre being produced against the        carcass assembly, wherein during the drum rotation the inflated        carcass assembly is partially joined with the belt-tread        assembly which rotates on the building drum together with the        inflated carcass assembly in the form of a toroid,    -   complete joining the belt-tread assembly with the carcass        assembly in the form of a toroid by stitching during rotation of        the building drum.

DISCLOSURE OF INVENTION

The above disadvantages are substantially eliminated by a method ofjoining a belt-tread assembly with a carcass assembly by stitching on atyre building drum in tyre production according to the presentinvention, the subject-matter of which consists in that a pressure isapplied in radial inward direction on the outer peripheral surface ofthe rotating belt-tread assembly connected with the carcass assembly inthe form of a toroid located on the building drum, the pressure beingexerted by at least two rollers, which are rotationally andinelastically disposed on a rigid bearing part of the stitching unit,which is provided with means for mutual symmetrical axial movement ofthe stitching rollers from the central part of the rotating outerperipheral surface of the belt-tread assembly of the tyre being producedto its shoulders, and possibly also with means for deflecting therotation axis of the stitching rollers from the position parallel to therotation axis of the tyre being produced, thus the rotation axis of thebuilding drum. The compressive force of the rollers is regulated(controlled) by means for moving the rigid bearing part in the directionof an axis perpendicular to the rotation axis of the tyre beingproduced. The means for moving the rigid bearing part in the directionof an axis perpendicular to the rotation axis of the tyre being producedserve also for bringing the rigid bearing part to a predeterminedposition at stitching, as well as for moving the rigid bearing part inthe course of the stitching process depending on the position of thestitching rollers on the rotational surface of the tyre being produced.

Radial movement of the stitching unit represents movement of the rigidbearing part in a direction perpendicular to the rotation axis of thetyre being produced. Radial movement of the stitching unit, provided inthe form of a rigid bearing part with at least two inelasticallyarranged stitching rollers, to a defined position, i. e. to a definedradial distance of the axis of the stitching rollers from the buildingdrum axis, is controlled automatically.

Likewise, the symmetrical movement of the stitching rollers in thedirection from the central part of the outer peripheral surface of thetyre being produced to its shoulders, i. e. in parallel to the axis ofthe rotating building drum, is controlled automatically, whereinsimultaneously also the rotation axis of the stitching rollers isdeflected from a position parallel to the rotation axis of the tyrebeing produced, so that the radial force, exerted in this way on theouter peripheral surface, can be utilized in a most effective way, andalso radial movement of the rigid bearing part is performed, so that themagnitude of the compressive force, exerted by the stitching rollers, ismaintained during the movement of the stitching rollers along the curvedouter peripheral surface of the tyre being produced.

The subject-matter of the present invention is also a device forstitching the belt-tread assembly onto the carcass assembly located onthe building drum containing driving means for rotating the buildingdrum, wherein the stitching unit comprises at least two stitchingrollers inelastically attached to the bearing part, the rollers rotatearound an axis which is parallel to the building drum axis, means forbringing the rigid bearing part to a predetermined position near therotating carcass assembly which is partially joined with the belt-treadassembly. These means serves also for moving the rigid bearing part withstitching rollers in the course of the stitching process depending onthe mutual position of the stitching rollers. The stitching devicefurther includes means for mutual symmetrical movement of the stitchingrollers from the central part of the outer peripheral surface of therotating tyre being produced to its shoulders after the stitchingrollers have contacted the above surface, and means for controlling thedeflection of the rotation axis of the stitching rollers from theposition parallel to the rotation axis of the tyre being produced,wherein the stitching rollers are constructed as inelastic.

Any known structural solution for the means for deflecting the rotationaxis of the stitching rollers from the position parallel to the rotationaxis of the tyre being produced can be used, provided that the stitchingrollers are attached in an inelastic way, that means they must not bedisposed, for example, on pneumatic cylinders.

The method of stitching the belt-tread assembly onto the carcassassembly in tyre production and a device, utilizing this method, will beexplained in more detail by means of attached drawings and examples ofembodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows schematically a side view of an arrangement of a deviceaccording to the present invention relative to the building drum.

FIG. 2 shows schematically possibilities of movement of separate partsof the stitching unit in the course of the process of stitching thebelt-tread assembly onto the carcass assembly according to the presentinvention.

FIG. 3 shows schematically a device for stitching the belt-treadassembly onto the carcass assembly according to the present invention.

FIG. 4 shows a stitching device according to the present inventionhaving a possibility to deflect the rotation axis of the stitchingrollers from a position parallel to the rotation axis of the tyre beingproduced.

FIG. 5 shows schematically deflection of a roller in radial directionwhen axially moving relative to the building drum axis in the case thatthe roller comes across a surface roughness

-   A in the traditional stitching method-   B in the stitching method according to the present invention.

FIG. 6 shows graphical representation of radial strength of a tyre,referred to as the so called “peak to peak” value

-   A in the traditional stitching method-   B in the stitching method according to the present invention.

EXAMPLES

The device, schematically shown in FIG. 1, consists of a building drum 9with lever arms, wherein the drum is provided with driving means,ensuring its rotation in a given direction and at a given speed. Aroundthe outer periphery of the building drum, there is wrapped a carcassassembly 1 over which a belt-tread assembly 5, prepared in advance, isbrought to a predetermined space. The building drum 9 is designed so asto be able to inflate the carcass assembly wrapped around it bycompressed air, wherein a certain pressure value is achieved. Throughinflating the carcass assembly 1 partial joining of the carcass assembly1 with the belt-tread assembly 5 is obtained and subsequent rotation ofthe building drum causes rotation of the carcass assembly 1 withpartially joined belt-tread assembly 5.

Near the building drum 9 a stitching unit according to the presentinvention is located, the unit consisting of a rigid bearing part 3, onwhich at least two stitching rollers 2 are disposed on supports 8, eachof the rollers being rotable around its own axis which is parallel tothe rotation axis A of the tyre being produced on the drum.

As can be seen in FIG. 2, the rigid bearing part 3 of the stitchingunit, and thus also the stitching rollers 2 may be radially moved duringthe stitching process in the direction of arrow 4. Besides the movementin the direction of arrow 4 the stitching rollers 2 can be axially movedin the direction of arrow 6, as well as their rotation axes can bedeflected in the direction of arrow 7 from a position parallel to therotation axis A of the green tyre being produced.

Referring to FIG. 3, the mechanisms of radial movement in the directionof arrow 4 of the rigid bearing part 3 of the stitching unit and ofaxial movement in the direction of arrow 6 of the stitching rollers 2will be described. The radial movement of the rigid bearing part 3 of adevice utilizing the method according to the present invention isensured by means of a servomotor 41, a threaded rod 43 connected withthe motor, and slides 42, wherein all these parts are arranged in radialdirection relative to the axis A of the building drum. Servomotor 41causes the threaded rod 43 provided with threading to rotate, causingthe bearing part 3 to move along the slide 42 radially towards the outerperipheral surface of the green tyre being produced. After completingthe stitching operation reverse motion of the servomotor 43 and thusrotational movement of the threaded rod 43 in the opposite directionmoves the stitching unit away from the green tyre produced. The sameprinciple has been used also for the axial movement of the stitchingrollers, wherein the arrangement of all parts, that is of the servomotor61, of the rod 63 joined with it and provided with right-handedthreading over one half of its length and with left-handed threadingover the other half of its length, and of slides 62, is parallel to theaxis A of the building drum. To ensure rotational movement of thestitching rollers 2 around their axis parallel to the axis A of thebuilding drum 9 it is preferred to locate the rollers on supports 8. Inthis way, the supports 8 have at their ends facing the building drumstitching rollers 2, which rotate around their axes when contacting therotating tyre being produced, and they are joined by their other endswith the rod 63 provided with right-handed threading over one half ofits length and with left-handed threading over the other half of itslength. In this case the action of servomotor 61 causes rotation of therod 63 provided with right-handed and left-handed threading, theconsequence of which is symmetrical movement of the supports 8 from thecentral part of the outer peripheral surface of the tyre being producedto its shoulders. Backward movement of the stitching rollers 2 isaccomplished by reverse motion of servomotor 61.

Deflecting the axes of stitching rollers from an axis parallel to therotation axis of the tyre being produced can be accomplished, forexample, in the way according to FIG. 4. On each of the supports 8,there is located an auxiliary support 82 which is joined with thesupport 8 through a pivoted joint 83. The end of the auxiliary support82 closer to the building drum 9 is provided with a pivotally attachedstitching roller 2. Linear servomotors 81 are joined with the supports 8and auxiliary supports 82 through pivoted joints. Throwing out pistonsof the linear servomotors 81 causes deflection of the stitching rollers2.

Exact positioning of the stitching rollers 2 by means of supports 8driven by the servomotor 61, of the bearing part 3 driven by theservomotor 41, pressure in the inflated tyre being produced, as well asthe speed of rotation of the building drum 9 are controlled by a controlsystem in such a way that perfect splicing between the belt-treadassembly 5 and the carcass assembly 1 is achieved in reasonable time.

Uniformity of tyres being produced is a quantity which can be assessedusing the value of radial force of the tyre as the so called “peak topeak” value. Therefore, the description includes also FIG. 5, whichshows schematically deflection of a roller in radial direction whenmoving axially relative to the building drum axis in the case, wherethis roller comes across a surface roughness in the traditionalstitching method and in the stitching method according to the presentinvention, and FIG. 6 which shows graphical representation of the aboveradial force of the tyre, indicated as the so called “peak to peak”value in the traditional stitching method and in the stitching methodaccording to the present invention. FIGS. 5 and 6 clearly show theadvantages of this invention in comparison with the background art.

1. A device for joining a belt-tread assembly with a carcass assembly bystitching in tyre production, characterized in that it comprises: arigid bearing part (3) at least two rotationally attached stitchingrollers (2), each of them being independently, inelastically and axiallymovably attached to the rigid bearing part (3), which is provided withmeans for axial mutually symmetrical movement of the stitching rollers(2), wherein the means are formed by at least one slide (62), arrangedin parallel with a rod (63), which is provided symmetrically from itscentre with threadings of opposite pitch sense and is joined with oneend of supports (8), which is adapted for symmetrical movement ofsupports (8) along the rod (63), controlled by a servomotor (61) foraxial mutually symmetrical movement of the stitching rollers (2), whichare rotationally attached at other ends of supports (8), wherein thestitching rollers (2) have an axis parallel to a rotation axis A of thetyre being produced, and inelastic means for moving the rigid bearingpart (3) in a direction perpendicular to the rotation axis A of a tyrebeing produced for bringing the rigid bearing part (3) to apredetermined position and to control compressive force of the rollerson the green tyre being produced, the means being formed by at least oneslide (42) parallel to a threaded rod (43), which is connected with aservomotor (41), wherein the threaded rod (43) together with the atleast one slide (42) is arranged perpendicularly to the rod (63)provided symmetrically from its centre by threadings of opposing pitchwith the proviso that the compressive force of the rollers is notinduced by pneumatic cylinders.
 2. A device for joining a belt-treadassembly with a carcass assembly by stitching in tyre productionaccording to claim 1, additionally comprising means for controllingdeflection of a rotation axis of the stitching rollers (2) from aposition parallel to the rotation axis A of the tyre being produced,which are connected with the respective supports (8), wherein each ofthe supports (8) is provided with an auxiliary support (82), provided atone of its ends with a one of said rotationally disposed stitchingrollers (2) and joined by the other end through a pivoted joint (83)with a linear servomotor (81), which is joined with the support (8)through said pivoted joint (83).
 3. A method of joining a belt-treadassembly with a carcass assembly by stitching in tyre production usingthe device according to 1, in which pressure is applied in radial inwarddirection on an outer peripheral surface of a rotating belt-treadassembly connected with an inflated carcass assembly of a tyre, which isdisposed on a tyre building drum, the pressure being exerted by said atleast two stitching rollers which are rotationally and disposed on saiddevice, wherein said device is provided with means for mutualsymmetrical inelastic and axial movement of the stitching rollers from acentral part of the outer peripheral surface of the belt-tread assemblyof the tyre being produced to edges of the belt-tread assembly, and withsaid means for moving the stitching rollers along an axis perpendicularto the rotation axis A of the tyre being produced, characterised in thatcompressive force of the rollers being controlled by inelastic means formoving the said rigid bearing part in the direction of an axisperpendicular to the rotation axis of the tyre being produced with theproviso that the compressive force of the rollers is not induced bypneumatic cylinders.
 4. A method of joining a belt-tread assembly with acarcass assembly by stitching in tyre production using the deviceaccording to claim 2, in which pressure is applied in radial inwarddirection on an outer peripheral surface of a rotating belt-treadassembly connected with an inflated carcass assembly of a tyre, which isdisposed on a tyre building drum, the pressure being exerted by said atleast two stitching rollers which are rotationally and disposed on saiddevice, wherein said device is provided with means for mutualsymmetrical inelastic and axial movement of the stitching rollers from acentral part of the outer peripheral surface of the belt-tread assemblyof the tyre being produced to edges of the belt-tread assembly, withsaid means for moving the stitching rollers along an axis perpendicularto the rotation axis A of the tyre being produced, and with said meanscontrolling the rotational position of the stitching rollers,characterised in that compressive force of the rollers being controlledby inelastic means for moving the said rigid bearing part in thedirection of an axis perpendicular to the rotation axis of the tyrebeing produced with the proviso that the compressive force of therollers is not induced by pneumatic cylinders.